The subject matter of this invention relates generally to metal clad switchgear and relates more particularly to metal clad switchgear with integral structural corner assemblies for making metal clad switchgear more useful.
Metal clad or metal enclosed switchgear as the case may be includes electrical circuit apparatus disposed within a metal cabinet in which high voltage electrical conductors are usually present. The metal cabinet is generally grounded so as to provide a surrounding region of zero electrical ground plane for the apparatus and conductors' protection. The electrical integrity of the ground plane or planes must therefore be relatively high. Furthermore, switchgear equipment is usually heavy. Consequently, the metal planes which define the top, rear, sides and back of the cabinet and the structural skeleton member upon which the planes are supported must accommodate stable mechanical loading and acceleration forces. This is even more critical in a situation involving similar vertically disposed switchgear elements where the structural skeleton, as opposed to the floor, must support all of the load of the topmost element. It has been found therefore that the construction of the eight corners of a metal enclosed or metal clad switchgear structural skeleton must assist in maintaining the structural capabilities of the skeleton and in maintaining the electrical integrity of the zero ground planes. Furthermore, for reasons of expense and efficiency the assembly operation should be simple and the form of the corner should be as uniform as possible for all eight corners to reduce the number of parts required for forming the eight corners of the skeleton. In much of the prior art the corner is merely formed by joining three perpendicular skeleton members one to the other without the aid of additional support members at the apex. Examples of such construction are found in the U.S. Pat. No. 3,275,394, entitled "Furnished Brace Construction", issued Sept. 27, 1966, to H. Massinger; U.S. Pat. No. 1,462,617, entitled "Interfitting Corner Construction", issued July 24, 1923, to E. Ohnstrand; U.S. Pat. No. 3,085,664, entitled "Frame Member", issued Aug. 16, 1963, to J. M. Adams et al.; U.S. Pat. No. 3,265,419, entitled "Cabinet Structure", issued Aug. 9, 1966, to J. A. Durnbaugh et al.; and U.S. Pat. No. 4,114,336, entitled "Electrical Switchboard Framework", issued Sept. 19, 1978, to H. L. J. Bechet et al. Furthermore, a slight deviation from the above-mentioned concept is taught in U.S. Pat. No. 3,110,535, entitled "Metal Cabinet Framework and Panel Structure", issued Nov. 12, 1963, to R. Q. Anderson et al. In the latter case a five-bend structure member is taught for convenient jointure with two other such members at a corner with the inclusion of a separate support block in the corner region. The support block in the latter case merely provides a convenient surface against which the other members may be welded or otherwise secured without providing significant separate support. In general, the preceding line of the prior art teaches a relatively simple construction in which welding or bolting of the members one to the other is required. In apparatus such as this no previously established unitary corner member is available upon which the corner may be constructed. In another line of prior art a basic corner member is provided upon which the strucutral skeleton members may be anchored. Such constructions are found in U.S. Pat. No. 2,167,525, entitled "Cabinet", issued July 25, 1939, to R. W. Rosendale and U.S. Pat. No. 3,919,603, entitled "Switchboard Framework Corner Tie", issued Nov. 11, 1975, to J. G. Salvati et al. In the latter case the corner member is constructed as a single folded sheetmetal member having slightly different configurations in one direction than in the others. Furthermore, the corner is not self-jigging, that is, the channel members must somehow be held in place on the corner member by separate apparatus or by construction personnel and then bolted or welded to the corner member as the case may be. In a further line of prior art the channel members are disposed upon a unitary corner and then a separate gusset is provided for completing the construction. In this case the corner constitutes a single folded sheetmetal piece and the gusset constitutes a separate piece. The latter line is exemplified by U.S. Pat. No. 3,353,854, entitled "Structural Corner Assembly", issued Nov. 21, 1967 to K. M. Hansen. In the latter two lines of prior art the folding operation associated with the construction requires at least two different setup operations because at least two different kinds of unitary corners are required. Furthermore, a separate gusset and tripodal member is required in each case. Finally, none of the members are self-jigging. It would be advantageous if a single member made of folded sheetmetal could be utilized to form all of the corner structures of metal clad switchgear and further included as part of the construction a gusset member and further be self-jigging.